Hi kaki3152, I think you are overestimating the speed lost due to the gondolas. Here's a test of a 109 with Mk108 gondolas, only 6 km/h speed loss is reported:
http://kurfurst.allaboutwarfare.com/...08gondies.html
Since also inner guns would result in increased wing drag, I would say that the variation between gondolas/integrated should be negligible.
The weight is really the issue here.
In fact, I would say that, in the 109 case, the gondolas is a better solution, allowing more
flexibility